1. Field of the Invention
The present invention relates to an apparatus for a sorting system and furthermore relates to a method for sorting by means of an apparatus according to the invention.
2. Description of the Prior Art
Today, apparatuses with discharge arms are used for sorting of items on a conveyor in connection with for example a belt weighing device, a grader, a sorter, a sizer, or similar machinery. Such discharge arms can work in two ways in that the discharge arm either draws or guides the item laterally off the conveyor, or the item is thrown off the conveyor.
In known apparatuses of the this type the discharge arms are pneumatically controlled with pneumatic cylinders connected to a central compressed-air unit supplying compressed air to the cylinders when the discharge arm is to be swung over the conveyor in order to catch an item.
In such known apparatuses having a discharge arm driven by a pneumatic cylinder, it is very difficult to obtain a uniform pressure in the pneumatic cylinders, since the mechanical friction may vary. This means that it is difficult to control the precise position of the discharge arm when it is being swung over the conveyor. As it is not possible to precisely control the position of the discharge arm, it may be difficult, irrespective of the lateral position of the item on the conveyor, to have the item led to the correct discharge position along the side edge of the conveyor, and consequently, there will be a high spillage percentage when the items hit the wrong place or are led to an incorrect discharge position.
A contributory cause of the fact that a pneumatic cylinder is not well-suited is that there is clearance and/or elasticity in the pneumatic cylinder, and a certain delay when compressed air is applied to it. Especially in conveyors where a number of apparatuses are provided in a row along the edge of the conveyor, it is a problem to apply pneumatically driven equipment because it is almost impossible to keep the same pressure level in all the cylinders. The uneven pressure depends on the capacity of the compressor and any leakages in the piping or hosing system between the apparatuses.